Annual medic and berseem clover dry matter and nitrogen production in rotation with corn

Annual medic (Medicago truncatula Gaertn.) and berseem clover (Trifolium alexandrinum L.) have potential to fix atmospheric N₂ for use by subsequent crops. Our objectives were to determine the dry matter and N production of annual barrel medic and berseem clover, and their effect on grain yield of a subsequent corn (Zea mays L.) crop. First-year treatments included spring-seeded annual medic-oat (Avena sativa L.) and berseem clover-oat intercrops; summer-seeded annual medic following spring-seeded oat; and a spring-seeded oat monoculture. The second-year corn crop was fertilized with four N rates. In three of four environments, berseem clover had greater average fall dry matter (4392 kg ha^-1) and N yield (125 kg ha^-1) than spring- or summer-seeded barrel medic. Spring- and summer-seeded medics had similar fall dry matter (1309 kg ha^-1 avg.) and N yields (38 kg ha^-1 avg.) in two environments, but spring-seeded medics had greater dry matter and N yield than summer-seeded medic in two environments (avg. dry matter yield of 5304 and 2428 kg ha^-1, respectively, and N yield of 138 and 70 kg ha^-1, respectively). Berseem clover and medic did not consistently differ in their effects on soil NO₃-N or corn grain yield when no N fertilizer was applied. Legume treatments increased second-year corn grain yields from 9% for the silt loam soil to 82% for the loamy sand soil compared with the nolegume treatment when no fertilizer N was applied; however, this effect decreased as N fertilizer rate increased.